Intermittent Parasitic Drain

[Aldous]

2005 X5 4.4

When I dont run my car for approximately 4 days (though once as short as 2) it won't start due to a dead battery. It's typically right dead, no interior lights, electric locks etc, no signs of life from the dash when turning the key. When i use the car regularly, couple drives a day, no problems at all, starts up quick with plenty of power etc.

I've had it in the shop, they tested the battery, it passed. Then they did a drain test and after the car goes to sleep the current being drawn drops to either 2 or 20 milliamp (cant remember which but the guy said it was the appropriate amount).

Something is likely waking up on the car at a later time and killing the battery. He mentioned that tracking it down in his shop would be time consuming and expensive so I'm hoping to try and figure it out myself.

The mechanic suggested it could be the FSR as this is a common problem and can cause this. He suggested I check the car occasionally while it's sitting and see if the fan is blowing, also when the climate control is set on auto to listen for quick increases and decreases in blower speed as this is an indication of a failed FSR. I've been reading this site and others and this does seem a likely suspect however i've been unable to catch the car waking up and blowing air, and the fan sounds quite steady when the climate control is on auto. What fuses could be pulled for 4 days to test if the FSR is the culprit?

I've also had a problem with the TCU, it froze and would pair to my phone, the mechanic took it out, replaced it with a new one, it worked. He plugged the old one back in and after the unplugging, it worked fine too (and has been since) however the fact that it locked up says something is wrong and i've read this can drain the battery as well (though not sure it would be intermittent, i would imagine it would be a steady draw and thus traceable). I tried pulling fuses 73 and 74 and the car still died, i think this rules out TCU

Any thoughts on testing? Is there any technology that would allow some continuous monitoring and recording of the power draw overnight for example? i was thinking of a multimeter and a video camera maybe?

Boosting it has been a pain, and with winter coming i really need to solve this.

Any help would be appreciated